mlx4: allow application to partially fork
mlx4: allow application to partially fork

Although using the PMD from a forked process is still unsupported, this
commit makes Verbs safe enough for applications to call fork() for other
purposes.

Signed-off-by: Olga Shern <94f6c1998eaef6808fd787423400815213eeb35d@mellanox.com>
Signed-off-by: Adrien Mazarguil <9d39ea493ca46c560334f650ac5d4b5ffbcb5cf0@6wind.com>

msune/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,tsphillips/dpdk-fork,msune/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,tsphillips/dpdk-fork,mixja/dpdk,mixja/dpdk,mixja/dpdk,msune/dpdk,mixja/dpdk,john-mcnamara-intel/dpdk